1. Field of the Invention
The present invention relates to a method of manufacturing a polysilicon film of a semiconductor device, and more particularly, to a method of manufacturing a polysilicon film used as a channel region of a thin film transistor.
2. Information Disclosure Statement
In general, the thin film transistor has the characteristics of high stability in data holding, high speed of operation and low consumption of current. The thin film transistor having such characteristics has been applied to highly integrated devices, such as a SRAM device and a LCD device. However, the thin film transistor has a disadvantage in that it has relatively low electrical performance since the polysilicon film is used as a channel region contrary to a general transistor which utilizes a mono crystal silicon film. To solve such disadvantage, a polysilicon film can be manufactured which has similar structure to the mono crystal silicon film. Therefore, research is being performed to increase the gain size of the polysilicon film to the maximum size.
In a method of manufacturing a polysilicon film according to a first embodiment of the prior art for forming a large grain size, an amorphous silicon film is formed in a temperature range of 450 through 550.degree. C. The amorphous silicon film is heat treated for a long period in a temperature range of 600 through 700.degree. C., whereby a solid phase growth (SPG) takes place and a polysilicon film of large grain size is manufactured.
However, since the polysilicon film manufactured according to the first embodiment has no uniformity in the size of the grains, electrical performance between dies or between cells in one wafer greatly varies. Due to the above described fact, the reliability and the mass productivity of the device is degraded. The polysilicon film manufactured by this method has a limitation in that the film can not obtain a grain diameter larger than 0.2 through 0.3 .mu.m.
In a method of manufacturing a polysilicon film according to a second embodiment of the prior art for forming a large grain size, a nucleus site is made by an ion implantation process in a surface portion of a substrate on which the polysilicon film is to be formed, the amorphous silicon film is formed by growing the amorphous silicon with the nucleus as a center, and thereafter the amorphous silicon film is heat treated, whereby a polysilicon film of large grain size is manufactured.
However, in this method, there are some difficulties in the depth control of ion implantation during the ion implantation process and in the density adjustment of the nucleus site. Furthermore, there is the possibility that the nucleus site can be lost during the cleaning treatment carried out after the ion implantation process. Due to the unstable process factors as described above, the reliability and the mass productivity of the device is degraded.